Polarization of Rayleigh scattered Lyα in active galactic nuclei

Abstract

The unification scheme of active galactic nuclei (AGNs) invokes an optically thick molecular torus component hiding the broad emission line region. Assuming the presence of a thick neutral component in the molecular torus characterized by a \ion{H}{I} column density > $10^{22}\mathrm{c}{\mathrm{m}}^{-2}$, we propose that far UV radiation around Ly$\alpha$ can be significantly polarized through Rayleigh scattering. Adopting a Monte Carlo technique we compute polarization of Rayleigh scattered radiation near Ly$\alpha$ in a thick neutral region in the shape of a slab and a cylindrical shell. It is found that radiation near Ly$\alpha$ Rayleigh reflected from a very thick slab can be significantly polarized in a fairly large range of wavelength $\Delta \lambda \sim 50$ Å exhibiting a flux profile similar to the incident one. Rayleigh transmitted radiation in a slab is characterized by the central dip with a complicated polarization behavior. The optically thick part near Ly$\alpha$ center is polarized in the direction perpendicular to the slab normal, which is in contrast to weakly polarized wing parts in the direction parallel to the slab normal. A similar polarization flip phenomenon is also found in the case of a tall cylindrical shell, in which the spatial diffusion along the vertical direction near the inner cylinder wall for core photons leads to a tendency of the electric field aligned to the direction perpendicular to the vertical axis. Observational implications are briefly discussed including spectropolarimetry of the quasar PG~1630+377 by Koratkar et al. in 1990 where Ly$\alpha$ is strongly polarized with no other emission lines polarized.

arXiv comment11 pages, 15 figures

References in corpus (21)

• Composite Quasar Spectra From the Sloan Digital Sky Survey
• The synthesis of the cosmic X-ray background in the Chandra and XMM-Newton era
• Revisiting the Unified Model of Active Galactic Nuclei
• Lyman Alpha Imaging of a Proto-Cluster Region at <z>=3.09
• A Subaru Search for Ly-alpha Blobs in and around the Proto-cluster Region at Redshift z=3.1
• Discovery of a Large ~200 kpc Gaseous Nebula at z=2.7 with the Spitzer Space Telescope
• A Lyman-alpha blob in the GOODS South field: evidence for cold accretion onto a dark matter halo
• Extended Lyman Alpha Nebulae at z ~ 2.3: An Extremely Rare and Strongly Clustered Population?
• Central Powering of the Largest Lyman-alpha Nebula is Revealed by Polarized Radiation
• A Pair of Compact Red Galaxies at Redshift 2.38, Immersed in a 100 kpc Scale Ly-alpha Nebula
• Strong Field-to-Field Variation of Lyman alpha Nebulae Populations at z~2.3
• The Polarization of Scattered Lyman Alpha Radiation Around High-Redshift Galaxies
• Mass without radiation: heavily obscured AGN, the X-ray Background and the Black Hole Mass Density
• The narrow Fe K$\alpha$ line and the molecular torus in active galactic nuclei - an IR/X-ray view
• Group-finding with photometric redshifts: The Photo-z Probability Peaks algorithm
• Stout: Cloudy's Atomic and Molecular Database
• A Successful Broad-band Survey for Giant Lya Nebulae I: Survey Design and Candidate Selection
• High Precision Analyses of Lyman alpha Damping Wing of Gamma-Ray Bursts in the Reionization Era: On the Controversial Results from GRB 130606A at z = 5.91
• A Polarimetric Search for Hidden Quasars in Three Radio Selected Ultraluminous Infrared Galaxies
• Asymmetric Absorption Profiles of Lyα and Lyβ in Damped Lyman Alpha Systems
• AGN Broad Line Regions Scale with Bolometric Luminosity

Cited by in corpus (9)

• Unlocking the Full Potential of Extragalactic Ly$\alpha$ through Its Polarization Properties
• Radiative Transfer in Lyα Nebulae: I. Modeling a Continuous or Clumpy Spherical Halo with a Central Source
• What Makes Ly$\alpha$ Nebulae Glow? Mapping the Polarization of LABd05
• Ly-alpha Radiative Transfer: A Stokes Vector Approach to Ly-alpha Polarization
• Lyman-$\alpha$ Polarization Intensity Mapping
• Little Red Dots as Direct-collapse Black Hole Nurseries
• Radiation-pressure Waves and Multiphase Quasar Outflows
• The polarized spectral energy distribution of NGC 4151
• Constraining the geometry of the gas surrounding a typical galaxy at $z=3.4$ with Ly$\alpha$ polarization